Search

Spectacular rock-cut landscapes consisting of closely spaced residual rock blocks separated by narrow intersecting corridors are variously termed as ‘rock cities’ and ‘ruiniform relief’. The former term has apparently never been formally defined except in the local Czech literature, whereas the latter was applied in various contexts, making the terminology confusing. This paper provides a global overview of forms, processes and controls behind such rock city/ruiniform landscapes and develops geomorphological terminology for such rock-cut landscapes, including the proposal that ‘rock city’ becomes a legitimate scientific term. Rock cities and ruiniform relief are two different types of rock erosional morphology, typified by the presence of a ‘street pattern’ in the former and highly weathered surfaces of rock residuals in the latter, although there is some overlap between the two. Examples of rock cities or ruiniform relief may be found in different lithologies and in a wide range of climates, from hyper-arid to humid. Classic localities include northern Czechia and adjacent parts of Poland and Germany, Australia, central Sahara, and the Gran Sabana in Venezuela. Lithologies particularly suitable to the development of this type of erosional morphology include mainly sandstones, followed by limestones, dolomites, conglomerates, tuffs, but igneous rocks such as granites or rhyolites are also known to support this type of relief. The combination of sufficient rock strength to support steep rock faces and the presence of discontinuities which, preferentially eroded, turn to ‘streets’ and ‘squares’ in the rock cities, appears as the basic prerequisite. A wide range of processes are involved in their formation, including surface and subsurface weathering, mass movements, salt tectonics, karst processes in both carbonate and silicate rocks, piping, fluvial erosion and aeolian abrasion. Despite being spectacular landscapes, very few models of long-term evolution of rock city and ruiniform relief have been presented in the literature and it is unlikely that any one scenario would apply to all situations. Rather, rock cities are examples of geomorphological convergence.

Aeolian processes, the entrainment, transport and deposition of sediments by wind, impacts climate, biogeochemical cycles, food security, environmental quality and human health. Considering the multitude of interactions between aeolian processes and all the major components of the Earth system, there is a growing interest in the scientific community to quantify the wind-related sediment movement process and redistribution rates at different spatial and temporal scales. However, this quantification is rather challenging, due to the complexities of physical mechanisms involved in aeolian processes and the inherent fundamental differences from the rather well-studied processes controlling fluvial erosion. Traditional techniques, such as erosion plots and surveying methods for monitoring wind erosion, are capable of quantifying sediment movement on small scales but they have a number of limitations in terms of the representativeness of the data obtained, spatial and temporal resolution and the patterns over extended areas, and the costs involved. The demand for alternative methods of soil loss and sediment redistribution assessment, in order to complement and enhance the existing methods, has directed attention to use tracing approaches for monitoring rates and spatial patterns of sediment redistribution at various scales. A comprehensive synthesis of available information from different scientific disciplines on aeolian tracer techniques, their applications and limitations are important in understanding the role of aeolian processes and their interactions with the Earths systems in changing climate and management scenarios. The objective of this paper is to provide a scientific review of the current tracer approaches in aeolian studies, including fallout radionuclides, rare earth elements, sediment finger printing and soil magnetism, as well as giving an introduction of the potential tracers that are in development.

Aeolian dust has a great influence on mountain hydrology, climate, and biogeochemical cycles. Dust deposited on glaciers and snowpack of the high alpine mountains in Tibetan Plateau (TP) and its surrounding regions can provide a unique method of determining the high-elevation transport and deposition of Asian dust in the middle and upper troposphere. Long-range-transported (LRT) Asian dust is often transmitted through the high troposphere, thus studies on dust deposition in the high-elevation cryosphere can reflect the LRT information of aeolian dust, and provide an unparalleled record to understand the regional climate and environment change in the “Third Pole” region. This paper comprehensively reviews the current status of the major factors that determine aeolian dust transport, settling, and cycling, and the key components of this dust cycles in high-elevation cryosphere regions, revealed by glacial snowpack and ice-core dust geochemistry recorded in the mountain glacier areas of TP and western China. Research on glacial dust concentrations indicated that much higher amounts of aeolian dust were found to transport and cycle in the high-elevation troposphere over TP and surroundings, compared to other locations of the globe. Dust concentrations and fluxes in high elevation regions of the TP were closely related to the transport distance of the nearby dust sources (e.g. large deserts and Gobi in western China, and arid deserts on the plateau surface). Isotopes tracers (e.g. 87Sr/86Sr, and eHf, eNd) and dust size distributions revealed that aeolian dust transported over TP mainly originated from the arid and semi-arid deserts and surface crust soils on TP; Aeolian dust from the large deserts of central Asia (e.g. the Taklimakan Desert with small ratio) have not been easily transported to the hinterland of TP under the current climatic conditions. An End-Member Mixing Analysis model was also used to calculate the relative contributions of northern hemisphere dust sources to the TP glacier dust sinks. The marked spatial differences in LRT dust sources of TP glaciers were caused by the large-scale atmospheric circulation strength and interactions in the Asian region. In addition, Asian dust has a large influence on the radiative forcing of glacier and snow melt in which the iron oxide composition constitute an important driving factor. Biogeochemical cycles in cryospheric regions were significantly affected by aeolian dust cycles, influencing glacial ecosystems, meltwater geochemistry (e.g. dFe release) and nutrients supply for downstream aquatic ecosystems. Ice core records for the past hundred years revealed a general decreasing trend of dust storm frequency and atmospheric concentration over the TP region. This work provides new insights and perspectives on aeolian dust transport and cycling in high regions of the troposphere and cryosphere of the TP, identifying critical uncertainties and priorities for future research.

Although it is commonly assumed that the trace-fossil record of eolian dunes and associated environments is invariably poor, a systematic review of the available information indicates that this is not necessarily the case. A model involving five main phases of colonization of desert environments through the Phanerozoic is proposed in this paper. The first phase (Cambrian-Silurian) involved animal incursions into coastal dune fields directly from the sea, although it is unlikely that these animals would have remained for long periods of time in coastal deserts. The second phase (Devonian) reflects the activities of dune pioneers that left their fluvial habitat to enter temporary or permanently into inland deserts. The third phase (Carboniferous-Permian) involved the colonization of deserts by tetrapods. The fourth phase (Triassic-Cretaceous) involved a major exploitation of the infaunal ecospace as reflected by the appearance of more varied behavioral patterns in sub-superficial structures. The fifth phase (Paleogene-Recent) reflects the appearance of the ecological dynamic that characterizes modern desert communities. The invertebrate ichnofacies for eolian dunes is re-named herein as the "Octopodichnus-Entradichnus Ichnofacies" honoring the seminal work of previous workers who simultaneously tackled the issue of eolian dune ichnofacies. The Chelichnus ichnofacies is retained for vertebrate trace-fossil assemblages in eolian settings. Both ichnofacies occur in mobile and temporary stabilized sandy substrates, subject to frequent erosion and deposition, and to strong seasonality. Desert settings consist of complex mosaics of habitats or physical units associated with organism activity. Trace-fossil distribution can be understood as reflecting the partitioning of desert settings in a mosaic of landscape units, characterized by water content and its temporal fluctuations, nutrient availability, nature of the substrate, and the dominant organisms present. In turn, desert systems are dynamic entities that change as a response to regional climate. Landscape units, such as eolian sand seas, salt flat and playa lake systems, ephemeral rivers and alluvial fans, interact in response to regional-scale climate variations in hyper-arid, arid, and semiarid climatic settings. Ancient deserts completely developed under hyper-arid climatic conditions rarely preserve trace fossils due to the absence of moisture near the surface. However, the alternation of wet periods may represent windows for life development and thus, preservation of biogenic structures. Arid deserts display complex patterns of dunes combined with dry, wet, and flooded interdunes. Dry desert elements (e.g. dunes, interdunes, sand sheets) typically record the Entradichnus-Octopodichnus and Chelichnus Ichnofacies. Slight rises in regional precipitation produce elevation of the water table and increase of fluvial discharges that provide water and sediment to the system. These processes may result in the local concentration of trace fossils in wet interdunes and ephemeral fluvial systems, illustrating the Scoyenia and Chelichnus Ichnofacies. In semiarid systems playa lakes expand by the addition of freshwater, evolving into freshwater lakes, and fluvial systems may become more common; lake margins and fluvial overbanks typically contain trace-fossil assemblages that may be ascribed to the Scoyenia Ichnofacies. Fil: Krapovickas, Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Mangano, Maria Gabriela. University of Saskatchewan; Canadá Fil: Buatois, Luis Alberto. University of Saskatchewan; Canadá Fil: Marsicano, Claudia Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina